The invention relates to a needle retracting mechanism for a hypodermic syringe, comprising a body with a needle retraction chamber, which body in a first end is adapted to receive injectant from a syringe barrel and in a second end slidingly supports a needle which by means of a force from a pretensioned actuator is retractable into the needle retraction chamber, the actuator being releasable by response to the injectant.
The invention also relates to a needle holder for a hypodermic syringe, which needle holder comprises a needle retracting mechanism.
The invention also relates to a hypodermic syringe comprising a barrel and a plunger, which syringe comprises a needle retracting mechanism.
Needles of used syringes constitutes a risk, both by themselves and as a source to contagion. Re-use of syringes constitutes a particular risk for contagion.
Most syringes are disposable syringes with a standardised fitting which can mate corresponding standardised fittings of syringe needles. This standardised fitting enables a wide range of combinations of various syringe sizes and needle sizes. A common standardised fitting is the Luer fitting.
Various safety syringes, in which the needle is retracted after use are known.
U.S. Pat. No. 5,122,118 describes an automatic needle retracting syringe in which a gelatine capsule retains a helical spring. Upon contact with the liquid injectant, the gelatine capsule weakens and allows the spring to retract the needle into the body of the syringe.
U.S. Pat. No. 5,049,133 describes a manual needle retracting syringe in which a spring which can retract the needle into the body of the syringe is releasable by moving the plunger to trigger a plurality of teeth-shaped hinges.
U.S. Pat. No. 5,188,614 describes a protective casing for use with a hypodermic syringe. A dual component foaming agent is disposed in the casing. When the components are mixed together they form an expanding and hardening plastic foam. Upon pressing the syringe into the casing subsequent to the ejection of fluid from the syringe, the foaming agents are activated and the expanding foam forces the syringe and syringe needle rearwardly within the casing, and encapsulates the used needle within the casing and foam.
WO-A-9 205 818 describes an automatic needle retracting syringe in which a spring which forces the needle into the plunger is released by pressing the plunger into the barrel after use.
WO 98/30261 describes a needle holder for use in combination with a syringe and a needle. The needle holder is provided with an expandable element and retention means for the expandable element. Contact between the expandable element and an injectant causes the expandable element to expand and retract the needle into the needle holder. The invention also relates to a syringe comprising the needle holder.
Prior art automatic needle retracting syringes which function by a response to the injectant, i.e. water, are generally encumbered with an unreliable and unpredictable release of the actuator.
Prior art manual needle retracting syringes are generally encumbered with the drawback that the force which is required to release the actuator is so large that using the safety syringe is felt cumbersome.
In some of the above mentioned safety syringes the needle and the retracting mechanism are integrated in the syringe barrel. There is therefore no possibility of combining variable syringe sizes with various needle sizes, which means that a greater number of syringe variants must be held in stock to satisfy all needs. Logistically this is a big problem.
A favourable material which respond to the injectant is alginate, which loses its mechanical strength and eventually dissolves in water. Alginate items are formed by extrusion or moulding. The resulting items are fragile and mechanically weak, which means that they easily deform or break. From a mechanical point of view, alginate is therefor not a preferable material.
The object of the invention is to provide an improved safety syringe in which the above problems are reduced or eliminated. Another object is to provide a safety syringe with both an automatic and a manual needle retracting mechanism. A further object is to provide an automatic needle retracting syringe in which alginate is suitable as material in the injectant responding item.
The objects are achieved by a needle retracting mechanism, a needle holder and a hypodermic syringe according to the preamble, which are characterized by the features of the claims.
In a first aspect the invention thus relates to a needle retracting mechanism for a hypodermic syringe, comprising a body with a needle retraction chamber, which body in a first end is adapted to receive injectant from a syringe barrel and in a second end slidingly supports a needle which by means of a force from a pretensioned actuator is retractable into the needle retraction chamber. The needle retraction chamber is provided with a funnel-shaped entrance opening, which widens out towards a retainer for the actuator and needle. The retainer comprises a compressible portion which in a retaining position is bigger than the entrance opening and abuts funnel-shaped sides of the entrance opening, and in a compressed release position is smaller than the entrance opening, and thus can enter the entrance opening. The pretensioned actuator forces the retainer into the funnel-shaped entrance opening, i.e. the actuator forces the compressible portion towards the release position. The compressible portion is, however, kept in the retaining position by a spacer. The spacer is made from a material which after some time in contact with the injectant loses its mechanical strength.
In storage no injectant is present, and the spacer maintains its mechanical strength and shape, which means that the compressible portion of the retainer is maintained in its retaining position.
When the syringe is filled with an injectant, a contact between the spacer and the injectant takes place, which after some time causes the spacer to lose its mechanical strength. The spacer then no longer maintain the compressible portion of the retainer in its retaining position, and the actuator therefore forces the compressible portion into the release position, and into the entrance opening. The width of the needle is smaller than the entrance opening, and both the needle and the retainer is forced through the entrance opening and into the needle retraction chamber. It is thus provided an automatic release of the needle retraction.
Preferably the compressible portion of the retainer comprises elastic arms which in first ends are integral with a base portion of the retainer and in second ends are moveable between the retaining position and the release position. The second ends of the elastic arms preferably have oblique end faces, corresponding to the funnel-shaped sides of the entrance opening. Further the elastic arms preferably have mountings for the spacer.
When the compressible portion of the retainer is in the retaining position and keeps the actuator in place, a force from the funnels-shaped sides of the entrance opening attacks the compressible portion of the retainer. This force is counteracted by a force from the compressible portion of the retainer, which force is a resultant of the force from the actuator and a force between the compressible portion and the spacer. Assuming no friction, the forces which act between the funnel-shaped entrance opening and the compressible portion of the retainer are perpendicular to the funnel-shaped sides. Depending on the angle of the funnel-shaped sides, which is a matter of design choice, the force between the compressible portion and the spacer can be made much smaller than the force from the actuator.
Practically there will be a friction between the funnel-shaped sides of the entrance opening and the compressible portion of the retainer, but still the force between the compressible portion and the spacer can be made much smaller than the force from the actuator by selecting the angle of the funnel-shaped sides.
For practical purposes, the injectant is an aqueous solution. Alginate has favourable characteristics with respect to dissolving in water, and is therefore well suited as a material for the spacer. As mentioned, alginate is, however, mechanically weak. In prior art automatic needle retracting mechanisms the item which loses its mechanical strength upon contact with the injectant is attacked by the force from the actuator, and alginate has thus not been suitable. In the inventive automatic needle retracting mechanism, the force which attacks the item which loses its mechanical strength upon contact with the injectant, i.e. the force between the compressible portion and the spacer, can be made much smaller than the force from the actuator by selecting the angle of the funnel-shaped sides, as discussed above. The invention thus enables the use of alginate in this item. The dissolving of alginate is reliable and predictable, and it is thereby provided a reliable and predictable automatic needle retraction.
In a preferred embodiment the needle retracting mechanism also comprises an inner sleeve which forms the needle retraction chamber and in an end proximal to the retainer is provided with the funnel-shaped entrance opening. The sleeve is movable relative to the body, towards the retainer. Further this embodiment includes an abutment which prevents the retainer from moving towards the second end of the body.
This embodiment enables a manual needle retraction by moving the sleeve towards the retainer. The retainer is kept in place by the abutment, and the funnel-shaped sides of the entrance opening, i.e. the end of the sleeve, presses the compressible portion of the retainer towards the release position. The spacer is mechanically weak, and is deformed or broken, whereupon the funnel-shaped sides of the entrance opening and/or the actuator forces the compressible portion into the release position and into the entrance opening. The actuator then forces the retainer and needle into the needle retraction chamber.
This embodiment thus provides a needle retracting mechanism which is both automatically and manually releasable. The manual release may be used if a quick retraction of the needle is preferred, or if the automatic release for some reason fails. The force which is required to deform or break the alginate during the manual release is moderate, as the alginate is weakened by the injectant. Thus the required force to produce a manual needle retraction is also moderate.
In a second aspect the invention relates to a needle holder for a hypodermic syringe, comprising a needle retracting mechanism according to the invention, as discussed above.
A first embodiment of the needle holder comprises the automatic needle retracting mechanism only, i.e. the first end of the body is adapted to match an outlet from a syringe barrel, and there is no sleeve.
A second embodiment of the needle holder comprises both the automatic needle retracting mechanism and the manual needle retracting mechanism, i.e. the needle holder also comprises a sleeve. The end of the sleeve distal to the retainer is adapted to match an outlet from a syringe barrel. The body of the holder is slideable on the sleeve, from an operating position in which the compressible portion of the retainer is in the retaining position and the needle is operable, to a retracted position in which the sleeve is moved towards the retainer, causing the release of the actuator and the retraction of the needle.
In a preferred embodiment of the needle holder, the body and the sleeve are relatively movable to a position in which the retainer is located in the first end of the body, the actuator is relieved and the needle is drawn into the body. This position is designated the extended position. Prior to using the syringe, the body is slid to the operating position, in which the retainer is located in the second end of the body, the actuator is pretensioned and the needle is operable.
In a third aspect the invention relates to a hypodermic syringe comprising a barrel and a plunger, with a needle retracting mechanism according to the invention, as discussed above.
A first embodiment of the hypodermic syringe comprises the automatic needle retracting mechanism only, in which the first end of the body forms an extension of the barrel.
A second embodiment of the hypodermic syringe comprises both the automatic and the manual needle retracting mechanism, i.e. the hypodermic syringe also comprises a sleeve. The first end of the body forms an extension of the barrel, and the end of the sleeve distal to the retainer forms an abutment for the plunger when the plunger is close to the bottom of the barrel, causing a further movement of the plunger into the barrel to force the sleeve towards the retainer, causing the release of the actuator and the retraction of the needle.